deps: upgrade npm to 6.5.0

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Where this should land

• Node 10
• Node 8

Notable Changes

This is a pre-release of npm@6.5.0 including a number of bugfixes and documentation updates.

• fc1a8d185 Backronym npm ci to npm clean-install. (@zkat)
• 89652cb9b npm.community#1661 Fix sign-git-commit options. They were previously totally wrong. (@zkat)
• d3e8a7c72 npm.community#2303 Make summary output for npm ci go to stdout, not stderr. (@alopezsanchez)

Another reminder that we've moved our issue tracking! You can read more about our move away from GitHub for issue tracking on our blog.

Changelogs

• 6.5.0-next.0